Good mouse, has 1 problem
The only problem I have with this mouse is the size and the hard textured cover for this mouse is also textured on the bottom section of the mouse. Since there is texture on the bottom of the cover, it slows the mouse movement down. A bit of sandpaper does take care of the problem though.

Too small
The Bad:
It's too small for medium to large hands, unless you're a claw-gripper. The smooth default grip is nearly useless unless you are a child or have small hands --- it's too small to palm, and too slippery and "velvety" to claw. So you'd spend more time trying to hold onto the mouse than actually working or playing. Sadly, the smaller interchangeable grip is the grip of choice if you're a palm-gripper, when it was designed for claw-grippers. The center of your palm will never be supported, leaving a gap of air.

The thumb-buttons are set too far back, causing me to retract my thumb before I can hit the "back" button with my thumb joint. This simply won't do for gaming. If I place my hand further back to accommodate the thumb buttons, then my palm won't be supported by the mouse at all, which makes me have to claw the mouse with my fourth and pinky fingers.

The Good:
Scroll wheel "MicroGear" works like a charm for scrolling quickly and stopping precisely at the portion of the page you want. This feature, along with Logitech's great mouse feet, makes it a little difficult for me to ditch the mouse.

Conclusion:
Since I still have my MouseMan Optical Dual Sensor mouse (Logitech), I periodically compared the grip comfort between the two mice. There is really no contest... the old old MouseMan's chassis is by far superior to the G9, for large and medium hands. There is definite palm arch support with the latter (and I suspect with the G5 as well). Whereas my hand (or any of my buddies') can't climb on the G9 at all and rest on top of it.

Get the G9 if you are a clawer. For palmers, look elsewhere. I'll be returning this unit before it causes me joint damage.

Middle Mouse Button Requires Force
In addition to all the other reviews, I'd just like to add that the middle mouse button is very difficult to press. It requires a ridiculous amount of force to push down. I died many times in various FPSs because I couldn't hit the middle quickly enough. Fortunately, this is fairly easy to fix: either change the middle mouse button to one of the secondary buttons using the downloadable software, or just change the key binds for any games you play. Other than that, this mouse is very good, and I'd recommend it to anyone who has the cash.

Awesome gaming mouse! A must buy!
This mouse is absolutely awesome. I've always been a fan of Logitech mice, having had a G7 and G5. I was looking for a new mouse and tried some of the Razer mice. I didn't find them comfortable at all and after using them for several days, they still didn't cut it. So I decided to try the Logitech G9, and I'm so glad I did.
First this mouse is extremely comfortable. I could just pick this mouse up and start playing, and didn't lose any of my previous accuracy in FPS. Anyone who has gotten a new mouse knows that it usually feels weird when you first get a mouse. This mouse just felt right. There was no adjustment period, it was just perfectly shaped for your hand.
Also this mouse is great for customizability, you have two grips, adjustable weights, and the software is very robust and lets you create profiles for mouse sensitivities and even changing the color of the LED.
The tracking on this mouse is perfect, I've never had the mouse skip on me, and I usually play FPS games like CS, COD4 and TF2. The construction of the mouse is top notch, I've had it for several months without any sign of wear to the grip or the bottom of the mouse. All in all a fantastic mouse. Definitely a 5 star product.

Overpriced lousy mouse
Being a fan of Logitech mx518, g5, and g7, I expected to like this newer g9 as well. Unfortunately I was quite disappointed. Both detachable hand grips are terrible. The first soft grip is designed so you have a move your whole arm for accurate movement. If you just use your fingers for mouse control like most other gamers, your grip on the mouse will slip occasionally. The second grip is designed for finger movements, but the actually feel is just awful. It feels like grinding your fingers against a sandpaper.

All the other feature felt like useless gimmicks to me. The features in G5 is more than I'll ever use so it's no surprise g9 is just pointless overkill. Is setpoint software seems buggy and takes time to load up well after the PC and Windows have loaded. The mouse does look quite ugly. Overall I feel Logitech's g5 and the optical mx518 are far better and comfortable to control than this mouse. G9 is so not worth the $99 MSRP price let alone the 40 bucks I paid for it.